The present invention relates to a magnetic tape data storage format, and more particularly, to storing data on a magnetic tape using a reverse concatenated modulation code with a low-density parity check (LDPC) code.
It has been projected that the capacity of magnetic tape cartridges will double every two years with an annual compounded growth rate of 41.42%, according to “International Magnetic Tape Storage Roadmap,” Information Storage Industry Consortium, September 2008. As the capacities increase, virtually all areas of tape recording systems will be improved in order to accommodate the additional storage. For example, improvements probably will be made to the recording media, the read/write heads, the recording channel, and servo technologies, and the overall data format.
For example, in the current generation of IBM 3592 and linear tape-open (LTO) tape drives, data is protected by two orthogonal Reed-Solomon error correction codes referred to as C1 and C2. Unencoded data is received by a write formatter and additional parity bytes are added according to the C1 and C2 encoding algorithm. Once the C1 and C2 parity bytes are added, the data is processed by a rate 32/33 run length limited modulation code.
After modulation encoding, the data is ready to be written to a magnetic tape. The problem with this architecture is that the modulation code is inserted between the error correction codes (ECCs) and the data as it is written on the magnetic tape. On the read side, modern error correction methodologies, such as LDPC codes or soft Reed-Solomon detectors, require that the information received from the data detector include the associated synchronous data samples. These data detectors are referred to as ‘soft detectors.’ It is not possible to perform soft detection using current data structures. This is because the data from the data detector is first processed by the modulation decoder and then processed by the C1 code. Any channel information relative to the detected bits is removed by the modulation decoder which simply outputs bits. Thus, soft detectors cannot be used with the current data format architecture. Accordingly, it would be beneficial to have a data format architecture which alleviates this problem.